In an avulsion fracture, a bone fleck or flake fractures from the main mass of the bone due to trauma to the bone. Avulsion fractures typically occur at joints where soft tissue, such as ligaments, is attached to protruding portions of the bone. The ligament can contract following the fracture and pull the fleck away from main bone mass. In reconstructive surgery, the fleck is held against the main bone mass with one or more set screws until the fleck fuses to the main bone mass. Bore holes for each set screw can be drilled into the bone fleck and the main bone mass for setting the set screw into the bone. After the bone fleck has fused to the main bone mass, the screws are commonly removed to permit the bone to heal and close the boreholes.
A disadvantage of set screws is the sizing of the boreholes that must be drilled for positioning the set screws. The set screws are typically 3-4 mm in diameter requiring similarly sized boreholes. If the bone fleck is too thin or small, the bone fleck can fracture or break into smaller fragments during drilling of the boreholes. As a result, surgeons often select thicker portions of the bone fleck that are sufficiently thick to receive a set screw. While minimizing the risk of fracturing or breaking the bone fleck, the positioning of the set screw can be less desirable for providing appropriate compression of the bone fleck to the main bone mass.